Why check prolactin levels in a female patient of reproductive age experiencing uterine cramping and potential hormonal imbalance?

Why Check Prolactin for Uterine Cramping

Prolactin should be checked in women with uterine cramping because hyperprolactinemia is a common, treatable cause of menstrual irregularities and anovulation, which can manifest as abnormal uterine bleeding patterns that may present with cramping. 1, 2

Primary Rationale for Prolactin Testing

Hyperprolactinemia directly causes reproductive dysfunction through disruption of gonadotropin-releasing hormone (GnRH) secretion, leading to:

• Anovulatory cycles with low mid-luteal progesterone (<6 nmol/L), which commonly present as menstrual irregularities including abnormal bleeding patterns 1, 2
• Oligomenorrhea, amenorrhea, or polymenorrhea - all of which can be associated with cramping and abnormal bleeding 1
• Infertility due to disrupted follicular maturation and corpus luteum dysfunction 3, 4

High Prevalence in Women with Menstrual Disorders

The evidence strongly supports routine prolactin screening:

• 61% of women with abnormal uterine bleeding have hyperprolactinemia, making it one of the most common endocrine causes 5
• Hyperprolactinemia affects approximately 90 per 100,000 women of reproductive age 6
• Only 48% of hyperprolactinemic women with bleeding disorders have galactorrhea, meaning the absence of galactorrhea does NOT exclude hyperprolactinemia 5

Specific Testing Protocol

Obtain a morning resting prolactin level (not postictal or after breast examination) with the following interpretation 1, 2:

• Prolactin >20 μg/L is abnormal and requires repeat testing 1, 2
• Repeat measurement is mandatory before diagnosis, as single elevations can be spurious 2
• Calculate as an average of three samples taken 20 minutes apart between cycle days 3-6 for greatest accuracy 1, 2

Critical Differential Diagnoses to Exclude

When prolactin is elevated, immediately evaluate for:

1. Hypothyroidism - TSH and free T4 must be checked, as primary hypothyroidism commonly causes hyperprolactinemia and menstrual irregularity 2
2. Prolactinoma - MRI of pituitary is indicated if prolactin remains persistently elevated to exclude micro- or macroprolactinoma 2, 3
3. Medication-induced - antipsychotics and other drugs can cause hyperprolactinemia 4, 6
4. PCOS - measure LH/FSH ratio (>2 is abnormal), testosterone, and mid-luteal progesterone, as PCOS commonly coexists with menstrual disorders 1, 2

Macroprolactinemia Caveat

A critical pitfall is macroprolactinemia - the presence of biologically inactive "big big" prolactin molecules that are detected by standard assays but cause no symptoms 3, 7:

• This explains cases of very high prolactin in normally ovulating women 3
• Macroprolactinemia does not require treatment and should be identified to prevent unnecessary interventions 7
• If prolactin is elevated but the patient has regular cycles, test for macroprolactin to avoid inappropriate treatment 7

Treatment Implications

If true hyperprolactinemia is confirmed:

• Dopamine agonists (bromocriptine, cabergoline) are first-line therapy and effectively normalize prolactin, restore ovulation, and resolve menstrual irregularities 8, 4
• Treatment prevents long-term complications including osteoporosis from chronic estrogen deficiency 3, 4
• If hypothyroidism is the cause, treating the thyroid disorder alone may normalize prolactin and restore regular menses 2

Additional Hormonal Workup

Concurrent with prolactin, measure 1, 2:

• Mid-luteal progesterone (day 21) - levels <6 nmol/L indicate anovulation 1, 2
• LH and FSH - to assess for PCOS (LH/FSH >2) or hypothalamic amenorrhea (low LH <7 IU/ml) 1, 9
• Testosterone and androstenedione - if signs of hyperandrogenism present 1, 2
• Fasting glucose/insulin - to assess insulin resistance associated with PCOS 1, 2